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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="checklist-gdkeventexpose-region"></a>Use GdkEventExpose.region</h2></div></div></div>
<p><b>Why. </b>
	The <em class="structfield"><code>region</code></em> field of
	<span class="structname">GdkEventExpose</span> allows you to redraw
	less than the traditional
	<em class="structfield"><code>GdkEventRegion.area</code></em>.
      </p>
<p>
      In GTK+ 1.x, the <span class="structname">GdkEventExpose</span>
      structure only had an <em class="structfield"><code>area</code></em> field to
      let you determine the region that you needed to redraw.  In GTK+
      2.x, this field exists for compatibility and as a simple
      interface.  However, there is also a
      <em class="structfield"><code>region</code></em> field which contains a
      fine-grained region.  The <em class="structfield"><code>area</code></em> field
      is simply the bounding rectangle of the
      <em class="structfield"><code>region</code></em>.
    </p>
<p>
      Widgets that are very expensive to re-render, such as an image
      editor, may prefer to use the
      <em class="structfield"><code>GdkEventExpose.region</code></em> field to paint
      as little as possible.  Widgets that just use a few drawing
      primitives, such as labels and buttons, may prefer to use the
      traditional <em class="structfield"><code>GdkEventExpose.area</code></em> field
      for simplicity.
    </p>
<p>
      Regions have an internal representation that is accessible as a
      list of rectangles.  To turn the 
      <em class="structfield"><code>GdkEventExpose.region</code></em> field into such
      a list, use <a href="../gdk/gdk-Points-Rectangles-and-Regions.html#gdk-region-get-rectangles"><code class="function">gdk_region_get_rectangles()</code></a>:
    </p>
<a name="gdkregion-get-rectangles"></a><pre class="programlisting">
static gboolean
my_widget_expose_event_handler (GtkWidget *widget, GdkEventExpose *event)
{
  GdkRectangle *rects;
  int n_rects;
  int i;

  gdk_region_get_rectangles (event-&gt;region, &amp;rects, &amp;n_rects);

  for (i = 0; i &lt; n_rects; i++)
    {
      /* Repaint rectangle: (rects[i].x, rects[i].y), 
       *                    (rects[i].width, rects[i].height)
       */
    }

  g_free (rects);

  return FALSE;
}
    </pre>
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